Cold email infrastructure boils down to the domains, mailboxes, and DNS records your campaigns actually depend on. Everything else in cold email sits on top of this layer, and the order you build it in genuinely matters — get it wrong and you'll spend weeks unwinding your own mistakes.
What follows is a build sequence starting from a blank slate. Follow it in order — each step assumes the one before it is already finished.
Defining infrastructure here
A cold email leaves from a mailbox, that mailbox sits on a domain, and that domain carries DNS records declaring who's allowed to send on its behalf. That stack, taken together, is your infrastructure. Your sending platform runs on top of it, but the platform itself isn't part of the infrastructure.
This topic earns its own guide because nearly every deliverability problem traces back to a decision made at this stage — the wrong domain choice, missing authentication, too few mailboxes carrying too much load. Build the base correctly and the rest of cold email gets noticeably easier from there.
Step 1: Choose your sending domains
Rule number one: your primary domain never touches a cold campaign. If a campaign dents your reputation, you don't want that damage anywhere near your main domain or the inbox your team relies on daily.
Instead, register dedicated sending domains, typically close variants of your brand name. Each one carries its own reputation, kept separate from your primary domain and from every other sending domain you own. Buy these well before you plan to send, since they need time to age and go through warmup before they're any use.
Step 2: Build out mailboxes
On each sending domain, create the actual mailboxes your campaigns will run through, hosted with a provider like Google Workspace or Microsoft 365.
Keep each mailbox's daily send count conservative. You scale cold email by adding mailboxes, not by leaning harder on the ones you've already got. A larger number of lightly loaded mailboxes is far safer than a small number carrying heavy volume. Run your own numbers with the free mailbox calculator.
Step 3: DNS and authentication
With domains and mailboxes in place, the next move is the DNS work that makes them trustworthy. This isn't optional, and it happens before anything ships.
- MX records so the domain can actually receive mail — necessary for replies and for looking like a legitimate, functioning domain.
- SPF, a single record listing every service permitted to send for the domain.
- DKIM, a signing key published for each sending platform you use.
- DMARC, a policy record, started in monitoring mode.
The SPF, DKIM and DMARC guide covers each of these in detail, and the free authentication checker confirms everything's passing before you move on. Don't skip verification — DNS misconfigurations fail silently and give you no heads-up at all.
Step 4: Ramp everything up
Domains and mailboxes exist at this point, but neither has earned any reputation yet. Sending real campaign volume right now would look identical to a spammer standing up disposable accounts.
Every mailbox needs a gradual ramp before it touches a live campaign — budget two to three weeks. The warmup guide covers the schedule in full, and a platform offering human-like warmup handles that ramp across every mailbox simultaneously instead of leaving you to manage each one by hand.
Step 5: Connect a sending tool
Only now does the sending platform come into play. It connects to your already-warmed mailboxes and handles campaigns, sequencing, and tracking on top of infrastructure you've already built.
This is also where the dedicated-versus-shared-IP decision gets made for you, whether you notice it or not. Plenty of platforms route everything through a shared IP pool by default, which means all the infrastructure work you just did ends up sitting on a reputation you don't fully control. Sendbox gives every account dedicated IPs and isolated infrastructure, and can provision mailboxes directly, so the whole stack stays under your control. The dedicated vs shared IP guide explains why that distinction matters.
Figuring out how many you need
The right count depends entirely on your target sending volume, which is exactly why the sequence in this guide matters as much as it does. You work backward from how much mail you actually need to move.
Start with a conservative daily send figure per mailbox. Divide your target daily volume by that number to land on how many mailboxes you need. Then spread those mailboxes across several domains so no single one is shouldering all the risk. The mailbox calculator does this math for you. Over-provisioning early is a common mistake — build for the volume you'll actually send over the coming months, warm it up properly, and expand domains and mailboxes as demand grows.
Infrastructure is the least glamorous part of cold email, and also the part that determines everything that follows. Build it once, carefully, in this order, and you'll rarely need to touch it again.